History of Astronomy

History of Astronomy

Ancient Astronomy Ancient cultures used the nighttime sky Arrival of seasons Astronomical events (eclipse) Seafarers-navigation Farmers-planting crops Constellations-way to label regions of celestial sphere Large and elaborate structures were built as calendars for the night sky

Stonehenge Salisbury Plain in England Believed to be an early astronomical observatory: Used as a calendar or almanac Identifies important dates through specific celestial events Built from 2800 B.C. to 1100 B.C. (17 centuries) Largest stones weigh 50 tons and were brought from many miles away

Astronomical Stone Alignment Many of the stones are aligned so that they point toward important astronomical events The line joining the center of the inner circle to the heel stone points in the direction of the rising Sun on the summer solstice (the longest day of the year) Alignments are related to the rising and setting of the Sun and the Moon at various other times of the year

Big Horn Medicine Wheel In Wyoming Used by Plains Indians Spokes are aligned with risings and settings of the Sun and other stars 10,000 ft atop Medicine Mountain

Caracol Temple Near Cancun, Mexico Built by the Mayans around A.D. 1000 Function to keep track of seasons and the heavens Windows are aligned with astronomical events such as sunrise and sunset at the solstices and equinoxes and the risings and settings of Venus Believed to be the activities of gods replaying mythical events from the time of Creation

Ancient Chinese Omens Comets-considered as omens guest stars -appeared suddenly and slowly faded away Kept extensive records of events 1054 A.D. best-known guest star visible in daytime sky for many months actually a supernova (star death) Part is still detectable today 9 centuries later Jesuits teaching astronomy in Chinese court

Ancient Chinese In ancient China, an astronomical observatory was usually built inside the capital city Trained astronomers were appointed to keep a diligent watch of the sky day and night They recorded important events (eclipses, comets, "new" stars...)

Arabic Astronomers New instruments Compass Rockets Mathematics Trigonometry Determine the precise dates of holy days Direction of Mecca from any given location on Earth Astronomical terms Zenith (point overhead) Azimuth (angle from the North) Star names Rigel, Betelgeuse, Vega

Study of the workings of the universe on the largest scale Today, cosmology entails looking at the universe on scales so large that even entire galaxies can be regarded as mere points of light scattered throughout space To the Greeks, however, the universe was the Sun, Earth, Moon, Mercury, Venus, Mars, Jupiter, and Saturn Cosmology

Geocentric Universe One of the earliest models of the solar system Developed by Greek philosopher Aristotle Earth is at the center of the universe All other bodies move around it in uniform motion

Planets Planets do not behave in as regular and predictable a fashion as the Sun, Moon, and stars They vary in brightness, and they don t maintain a fixed position in the sky They seem to speed up and slow down during their journeys, and at times they even appear to loop back and forth relative to the stars

Problems with Geocentric Model Geocentric model could not account for: Variations in planetary brightness The planets produce no light of their own Retrograde motion There are periods when a planet s eastward motion stops and the planet appears to move westward in the sky for a month or two before reversing direction again and continuing on its eastward journey http://www.astro.uiuc.edu/p rojects/data/retrograde/

More Complex Model New model developed Each planet moves around a small circle called an epicycle Epicycle center moves uniformly around Earth on a second larger circle known as the deferent Motion composed of 2 separate circular orbits http://www.astro.utoronto.ca/~zh u/ast210/geocentric.html

Ptolemy s model A.D. 140 Explained paths of the 5 known planets, Sun & Moon Eccentric = true center (black dot) Planet moves uniformly in relation to the aequant (orange dot) Required 80 circles to account for the paths http://webpages.charter.n et/middents/ptolemy's%2 0Model.htm

Aristarchus The first to propose a heliocentric or sun-centered theory of the universe Used eclipses to estimate the sizes and distances of the Earth, Moon and Sun. Looked at the Earth's shadow on the Moon during a lunar eclipse Curve of the Earth's shadow on the Moon indicated that the Earth is larger than the Moon-- over twice the size The Moon's shadow on the Earth was smaller because solar eclipses were rare events and observed in some parts of the extensive Greek Empire but not other areas Solar eclipses showed that the Earth had to be much bigger than the Moon

Aristarchus Measured distance to the sun with geometry Showed the Sun was 20 times farther from the Earth than the moon Helped show the sun was the center of the universe His ideas were not accepted until 16 th century because Aristotle had too much influence

Renaissance Science

Copernicus Ptolemy s model of the universe survived for 13 centuries Rediscovered Aristarchus s heliocentric model

Copernican Revolution Foundations: 1. Earth is not at the center of everything 2. The center of Earth is not the center of the universe it s the center of gravity & lunar orbit 3. All planets revolve around the Sun 4. The stars are farther away than the sun 5. Apparent motion of the stars is a result of Earth s motion 6. The motions of Earth are responsible for the Sun s daily and yearly motion 7. Heliocentric model explains the retrograde motion of the planets

Retrograde Motion When Earth & Mars are close Mars is brighter When farther apart appears dimmer Because line of sight from Earth to Mars changes as the planets orbit Sun, Mars looks like it loops back & forth in retrograde motion Line of sight changes because Earth moves faster in orbit than Mars http://csep10.phys.utk.edu/astr16 1/lect/retrograde/copernican.html http://www.lasalle.edu/~smithsc/ Astronomy/retrograd.html

Unaccepted Model Neither his fellow scholars nor the general public easily accepted Copernicus s model Renaissance science was a time when logic and deduction were seen as secondary to intuition and emotion. Heliocentricity violated many of the religious teachings of the time It demoted Earth to a noncentral and undistinguished place within the solar system and the universe Copernicus s work had little impact on the general populace of his time, at least in part because it was published in Latin (the standard language of academic discourse at the time), which most people could not read Only long after Copernicus s death, when others popularized his ideas, did the Roman Catholic Church take them seriously enough to bother banning them

Modern Astronomy

Galileo Galilei Italian mathematician and philosopher Used the newly invented telescope for experimentation Built his own telescope in 1609 View of skies supported Copernicus

Galileo s discoveries Mountains, valleys, and craters on the Moon Sunspots on the Sun (looking at the Sun may have been cause of blindness) Determined the Sun rotates about once per month around an axis because of the changing appearance of sunspots from day to day Observed the phases of Venus Galileo s drawings of the moon and sunspots

Galileo s discoveries Saw four small points of light around Jupiter in night sky Decided they were moons Because another planet was at the center of the moons supported Copernican model it proved that Earth is not the center of the universe

Galileo Galileo was directly challenging both the scientific orthodoxy and the religious dogma of his day A few years earlier, an astronomer was burned at the stake in Rome for teaching the Earth orbited the Sun

Galileo 1610-published conclusions that supported Copernicus 1616-Roman Catholic Church instructed him to abandon astronomical research because it went against literal view of the scriptures 1632-published a book that compared Ptolemaic and Copernican models written in Italian not Latin, which brought him into direct conflict with the Church Forced to retract his claim during the Inquisition 1633-placed under house arrest 1638-went totally blind Remained under house arrest until his death in 1642 1992-Church publicly forgave Galileo

Proof Renaissance scholars were correct, but they could not prove that our planetary system is centered on the Sun, or even that Earth moves through space Direct evidence for this was obtained only in the early eighteenth century, when astronomers discovered a shift in the observed direction to a star, caused by Earth s motion Further verification of the heliocentricity of the solar system came gradually, with innumerable observational tests that culminated with the expeditions of our unmanned space probes of the 1960s, 1970s, and 1980s